Merge r572000 from trunk:

* Fix proxy-sendchunk(s|ed) problem.

PR: 43183

Submitted by: Brian Rectanus <Brian.Rectanus breach.com>, Vincent Bray
Reviewed by: niq, rpluem, fielding


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@572421 13f79535-47bb-0310-9956-ffa450edef68